1. Field of the Invention
This invention relates in general to earth drilling devices and methods and in particular to core sampling devices and methods.
2. Description of the Prior Art
Earth drilling machines which incorporate the use of core sampling equipment are well known for taking geological samples of earth layers. One method of obtaining a core sample has traditionally involved attaching a drill bit device to the spindle of a drilling machine, drilling a hole in the earth and then forcing a sampling tube into the earth at the bottom of the drill hole. This method is satisfactory when the depth of the drilled hole is shallow inasmuch as only one or two drill sections may have to be attached in order to reach the desired depth. However, for deeper holes a series of drill sections have to be connected together, then prior to taking a sample, a sampling tube is lowered into the drilled hole by means of drill rods which must be threaded together to extend the depth of the hole. The activity of threading the drill rods together and then taking them apart when the core sample is retrieved from the hole results in a considerable amount of time being spent in handling the rods.
One solution to this problem of having to connect and disconnect a series of drill rods each time the sampling tube is lowered into and retrieved from the hole is provided by the open spindle concept which allows the sampling tube to be lowered through a series of hollow drill sections into the hole by means of a reelable hoist cable. The device of Davis, U.S. Pat. No. 3,794,127 discloses such an open spindle drilling machine which uses an auger style drilling section which has a helical flight for bringing soil from the bottom of the hole to the surface. Once the hole is drilled to the desired depth, a sampling tube is lowered through the hollow auger sections to the bottom of the hole and is driven into the earth by means of a hammer which is lowered to repeatedly strike the top of the sampling tube.
Related open-spindle drilling devices are disclosed by the patents of Frenzel, U.S. Pat. No. 2,145,170; Kinnear, U.S. Pat. No. 2,251,679; Pickard, U.S. Pat. No. 3,120,282; Wolda, U.S. Pat. No. 3,739,865; and Sweeney, U.S. Pat. No. 3,893,524. Each of these devices allows the operational advantage of being able to position the sampling tube at the bottom of the drilled hole without having to connect and disconnect a series of drill rods. However, these referenced devices are limited by their construction to core sampling of rock or solid soil formations. Such devices are not suitable for taking and retrieving of relatively undisturbed soil samples suitable for laboratory tests according to ASTM Designation: D1587-67. This ASTM designation requires that a thin-walled tube be used and that the tube be inserted into the soil with continuous and rapid penetration and without impact or twisting. In each of the referenced devices, the sampling tube is attached to the drill section in such a way that as the drill section rotates, the sampling tube also rotates and thus, there is a twisting motion as the tube enters the soil being sampled and consequently, such devices are not suitable to obtain a relatively undisturbed soil sample as the ASTM designation requires.
The devices of Hansen, U.S. Pat. No. 1,456,983 and Castel et al., U.S. Pat. No. 3,870,112 are designed in such a way as to be usable for taking relatively undisturbed soil samples. Hansen incorporates an outer drilling tube bearingly mounted around an inner sampling tube. The outer drilling tube has a spiral conveyor formed on its inner wall for removing debris as the drill bit rotates and the inner sampling tube is nonrotatable. The disadvantage with both Hansen and Castel is that neither device uses an open-spindle design. Consequently, the taking of a sample with the Hansen and Castel devices is a relatively complicated and time-consuming procedure.